题目不对,应该是COS（2A）+COS（2B）=2cos（A+B）*cos（A-B）根据：cos(x+y)=cosxcosy-sinxsinycos(x-y)=cosxcosy+sinxsiny得：cos(x+y)+cos(x-y)=cosxcosy-sinxsiny+cosxcosy+sinxsiny=2cosxcosy令x=X+Y y=X-Y得：X...